1. Field of the Invention
The present invention relates to a method of manufacturing a microlens array and a projection type of liquid crystal display apparatus, and relates to a technology which is applied to, for example, an image projecting device including a liquid crystal panel and so on.
In the invention, a term of ‘a cylindrical shape’ is a synonymous with a partially cylindrical shape.
2. Description of the Related Art
Liquid crystal display apparatuses are generally classified into a direct-view type and a projection type.
For example, in a liquid crystal projector or the like, one of a projection type which projects the content of a display cell on a screen by the use of a lens, the projection-type one facilitating large screen display, is used. As compared with a projection type of cathode ray tube display apparatus, this projection type of liquid crystal display apparatus has a broad color reproduction range, and is small and lightweight, and therefore, it is excellent in portability. Because an optical system of a projection type of liquid crystal display apparatus is not influenced by geomagnetism, a convergence adjustment, that is, a color deviation-correction is unnecessary in a projection type of liquid crystal display apparatus. Because a projection type of liquid crystal display apparatus is provided with the aforementioned features and made to be a large screen more easily than one of a direct-view type, it is thought to become major in household image display apparatuses.
Projection-type color image display systems using liquid crystal display elements are divided to a three-panel system using three liquid crystal display elements corresponding to the three primary colors and a single-panel system using one liquid crystal display element. In the structure of a three-panel system of image display system, an optical system which divides white light into the three primary colors of red, green and blue and three liquid crystal display elements which control light fluxes of the respective colors and form images are disposed independently from each other, and images of the respective colors are optically superimposed and displayed in full colors.
In the structure of a single-panel system of image display system, a color filter of the three primary colors is placed in each pixel, and a color image is projected by one liquid crystal display element. Since this single-panel system uses only one liquid crystal display element and the structure of an optical system is simple as compared with that of the three-panel system, it is possible to reduce the component count of a projection type of liquid crystal display apparatus and decrease the cost of manufacturing, and moreover, it becomes possible to downsize.
A projection type of liquid crystal display apparatus equipped with a single-panel system of liquid crystal display element, the projection type of liquid crystal display apparatus having no color filter, which is so-called color-filterless (refer to Japanese Unexamined Patent Publication JP-A 7-181487 (1995), page 7, FIG. 1), for example), is disclosed. In the liquid crystal display element, a first microlens array is bonded on one end face on a light-entering side of a board. On the other end face on a light-exiting side of the board, a second microlens array is bonded.
By three dichroic mirrors which are not shown in the drawings, white light from a white light source is divided into respective colors of red R, green G and blue B. Light fluxes of the respective divided colors are converged in the vicinity of a light-exiting position of the second microlens array by the first microlens array. The second microlens array parallelizes chief rays of the plural entering light fluxes and makes them exit from the liquid crystal display element. The first and second microlens arrays are manufactured, respectively, by the use of a thermal sagging method, an ion exchange method, a thermal transfer method, a machining method or the like, and by bonding the manufactured first and second microlens arrays to the board while aligning the optical axes thereof, a two-layer microlens array is manufactured.
Various manufacturing methods of manufacturing two-layer microlens arrays are proposed (refer to Japanese Unexamined Patent Publication JP-A 2000-98102 (2000), page 8, FIGS. 13–16, for example). In a manufacturing method disclosed in the Japanese Unexamined Patent Publication JP-A 2000-9810.2 (2000), page 8, FIGS. 13–16, a two-layer microlens array is molded by a so-called 2P (2P: photo polymerization) method using an ultraviolet curing resin that is cured by irradiation of an ultraviolet ray. In specific, a vertically driving mechanism that is capable of vertically driving is disposed to a board that is supported by a table.
In a state that a stamper is adhesively supported by this vertically driving mechanism, an ultraviolet curing resin is supplied between the stamper and the board, the vertically driving mechanism is driven, and the supplied ultraviolet curing resin is molded into a desired shape by the stamper. After that, the ultraviolet curing resin is cured by irradiation of an ultraviolet ray, and the stamper is released by the vertically driving mechanism. By repeatedly executing the operation of supplying the resin, molding by the use of the vertically driving mechanism and the stamper, curing with an ultraviolet ray and releasing the stamper, a two-layer microlens array is molded between two boards.
In the related art of the three-panel system described above, it is possible to effectively use light emitted from a white light source and the purity of color is high, whereas since a color separating system and a color synthesizing system are necessary, an optical system is complicated and the component count increases. Therefore, in the case of this projection type of liquid crystal display apparatus, not only the cost of manufacturing is high, but also a manufacturing method is complicated.
In the related art of the single-panel system using a color filter, it is possible to decrease the cost of manufacturing and downsize as compared with the related art of the three-panel system, whereas since light is absorbed or reflected by the color filter, for example, only approximately one third of incident light can be used. Therefore, the efficiency of use of light is bad, and a display screen is dark.
In the related art disclosed in JP-A 7-181487, it is possible to make a display screen brighter by disposing the second microlens array, whereas when bonding the first and second microlens arrays to the board, it is required to align them so that the centers of a plurality of lenses of a minute lens pattern of the first microlens array match with the corresponding centers of a plurality of lenses of the second microlens array. Because this alignment of the first and second microlens arrays is difficult and a highly accurate aligning device and a bonding device are necessary, the cost of equipment is high.
In the related art disclosed in JP-A 2000-98102, the stamper is moved plural times by the vertically driving mechanism to produce the first and second microlenses. The vertically driving mechanism has, for example, a direct acting bearing whose straightness is high, and the accuracy of alignment of the first and second microlenses is substantially determined by the straightness of the direct acting bearing. However, even when the direct acting bearing with high straightness as described above is adopted, it is difficult to restrict the alignment accuracy within 10% of a pixel pitch, which is a necessary specification. In a case where the alignment accuracy of the first and second microlenses deviates from a necessary stipulated value, not only the efficiency of use of light decreases markedly, but also a light flux undesirably enters into an adjacent pixel. As a result, so-called color mixture is caused, and the quality of an image is lowered significantly.
Moreover, in order to minimize a deviation of the first and second microlenses, it is necessary to mold the second microlens in the state of supporting the board and the stamper to the device after molding the first microlens. As a result, the shape of the first microlens and the shape of the second microlens become the same shapes inevitably. Therefore, freedom of design is considerably restricted, and it is impossible to realize a two-layer microlens array that enables acquirement of optimum efficiency of use of light. Since freedom of design is thus restricted considerably, it is impossible to manufacture the two-layer microlens array disclosed in JP-A 7-181487 by using the related art
Further, in the related art disclosed in JP-A 2000-98102, page 8, FIGS. 13–16, it is necessary to increase refraction indices in the order of the first microlens, the second microlens and the board. However, since the width of the refraction index of a UV (ultraviolet) resin has a limitation, a sufficient difference of refraction indices cannot be obtained on lens faces, and a lens with a short focal length cannot be produced.
Furthermore, in the 2P method or an injection molding method, it is difficult to form a vertical wall between adjacent microlenses. Even when the vertical wall can be formed by the use of the 2P method or the injection molding method, there is a problem that the vertical wall, that is, the microlenses themselves are broken at the time of mold release.